As well known, footwear is used to protect a wearer's feet and is manufactured and sold in various forms and kinds. In generally, the footwear includes: an upper for covering and protecting the top of the foot and the ankle; and a sole for protecting the sole of the wearer's foot and increasing a frictional force between the footwear and the ground to thereby improve the wearer's walking performance and relieve the shock applied to the sole of the wearer's foot while walking.
Moreover, the sole includes: an insole that is the interior bottom of the footwear; a midsole that is made of rubber, foamed resin or sponge with an excellent buffer power to resiliently disperse and support the wearer's weight; and an outsole that is attached to the bottom surface of the midsole and is made of rubber material to provide a frictional force while the wearer walks. As described above, the upper, the midsole and the outsole are separately manufactured and joined together through the processes of cleaning, priming and bonding.
In the meantime, Korean Patent No. 10-0978284 discloses a method of manufacturing footwear including an outsole, a midsole and an upper in detail. Referring to FIG. 8, the method of manufacturing footwear disclosed in Korean Patent No. 10-0978284 will be described in detail.
As shown in FIG. 8, first, a method of manufacturing the midsole includes the steps of: forming the outsole by putting a rubber sheet in a mold and pressing it at high temperature and high pressure; buffing to make the surface of the outsole rough in order to increase an contact area between the outsole and the midsole; cleaning the molded outsole with aqueous alkali cleaner (pH 10 to 12) (or hydro-cleanser, in which is mixed with water) for five to ten minutes using a cleaning machine; coating aqueous or oil primer containing acetone so that adhesive is smoothly applied onto the surface of the outsole; drying the coated outsole; applying the adhesive; and drying.
Next, a method of manufacturing the midsole includes the steps of: putting a raw material (generally, EVA) in a press phylon mold or a CMP (Compressed Molded Phylon) mold to mold a pre-foamed midsole; putting the pre-foamed midsole into another phylon mold to complete the shape of the phylon midsole, wherein the midsole molding process generally includes three or two steps of foaming EVA of a biscuit form in such a way as to be about 190 percent larger than the actual size of the midsole, forcedly putting the foamed EVA into a phylon mold, and forcedly press-molding it to become a midsole of the actual size; cleaning the midsole with water of 40° C. to 60° C. for 5 minutes to 10 minutes using a cleaning machine; coating with UV primer and radiating UV rays to modify the coated surface of the midsole so that the midsole and the upper can be bonded firmly; coating the surface of the midsole with aqueous primer and adhesive; and drying the midsole.
Next, a method of manufacturing the upper includes the steps of: cutting woven fabric or leather to form the upper; cleaning the upper with methyl ethyl ketone (MEK) so that the upper and the midsole can be bonded firmly; coating the upper with aqueous primer; drying the coated upper; applying adhesive to the upper; and drying the upper.
After the outsole, the midsole and the upper are manufactured through the above processes, when fixed heat and pressure are applied in a state where the outsole and the midsole are put in a mold in order, the midsole and the outsole are bonded together, so that the sole having the midsole and the outsole is manufactured.
After bonding of the midsole and the outsole is completed, when fixed heat and pressure are applied in a state where the sole and the upper are put in a mold in order, the sole and the upper are joined together, so that the footwear is completely finished.
However, the conventional method of manufacturing footwear including the above processes has several problems as follows.
First, as described above, there are many environmental obstacles, consumption of many raw materials, and a great deal of processes in manufacturing the outsole, the midsole and the upper, and it causes deterioration of productivity and increase of manufacturing costs.
For instance, in the case of the buffing process of making the surface of the outsole rough in order to increase a contact area between the midsole and the outsole, it aggravates working environment because dust of rubber, which is a material of the outsole and is harmful to the human body, is generated. Furthermore, in order to remove foreign matters stained on the outsole, a worker has to use aqueous alkali cleaner (or water and hydro cleanser) using a separate cleaning machine, and hence, it has several problems in that additional costs are incurred due to purchase of machines, footwear manufacturing processes are increased, and it requires a lot of manpower.
Second, the above problems are incurred also when the midsole is manufactured.
Third, when the outsole, the midsole and the upper are manufactured, all of the manufacturing methods require the process of coating UV primer or radiating UV rays and coating primer containing acetone and the process of applying adhesive in order to achieve a firm bonding, however, the processes increase the manufacturing costs due to a lot of manpower and increase of footwear manufacturing processes (namely, the primer coating and adhesive applying processes).
Fourth, solvents used for the UV primer coating, UV radiating, and acetone-containing primer coating processes may damage the worker's eyes, irritate the skin, cause respiratory irritation and nausea, sickness, and sleepiness and affect lungs when the worker inhale the solvents, and cause paralysis and convulsion as long-term symptoms, and hence, the solvents may give the worker a fatal damage.
Fifth, according to the conventional footwear manufacturing method, the outsole, the midsole and the upper are separately molded and are bonded together through a great deal of processes, such as cleaning, primer coating, adhesive applying, drying steps, and hence, it causes deterioration of productivity and increase of manufacturing costs due to a lot of raw materials and manpower.